Silicone-based release coatings are useful in applications where relatively non-adhesive surfaces are required. For example, pressure sensitive adhesive labels may have a backing sheet that has applied thereto a silicone-based coating to retain the labels without affecting the adhesive properties of the labels.
For example, for the preparation of pressure sensitive adhesive labels, a paper layer such as glassine, wood free paper or kraft paper, is coated with a silicone-based film. The silicone film is then adhered to by the adhesive material of the label stock. The silicone-based release film allows the adhesive material of the label stock to be easily removed and for the label stock to still retain its adhesive characteristics.
The typical methods for providing release papers for adhesives is based on three chemistries: silicone, chrome complex and polyethylene (PE). None of these treatments allow the backing paper to be recycled.
In addition, there are three different silicone types: solvent based, solventless or water-based. Solvent based technology requires a solvent recovery system so that the solvent does not escape to the environment causing pollution and to make the process economical. Solventless technology is expensive and the catalyst can be easily inactivated by minor contaminants. Solvent-based and solventless technologies both produce a backing paper which is not repulpable or recyclable. Water-based silicone technology can provide performance for a broad range of adhesives, but the resulting backing paper is not repulpable or recyclable. The chrome complexes, some of which can be considered as having non-objection status from the FDA for food contact, still represent a potential environmental hazard because of their chromium content.
PE is not recyclable and like the chrome complex, does not provide performance to a broad range of adhesives, especially the more aggressive types.
Published PCT Application WO2008/019953 teaches a polyorganosiloxane based release coating composition which can be used to coat polyester films.
Published PCT Application WO 2010/012787 teaches a liquid silicone composition for coating a number of substrates, including polyethylene terephthalate type polymer films.